Method of conveying breathing gases to or from a patient

ABSTRACT

A method of conveying humid breathing gases from a patient through a breathable breathing tube. The breathing tube includes a heater associated, at least in part, with a portion of hydrophilic material. The purpose of the heater is to evaporate any condensed liquid collecting in the conduit, which is first sucked tip by the hydrophilic material. The heated wick reduces the risk of collected water being passed to the patient and causing choking fits or discomfit. It is preferred that the heated wick lies freely in the conduit to settle at low points in the conduit where condensation may collect.

This application is a divisional of U.S. patent application Ser. No.10/649,938, entitled “Conduit with Heated Wick” which was filed on Aug.27, 2003, which is a continuation of U.S. patent application Ser. No.09/886,835, entitled “Conduit with Heated Wick” which was filed on Jun.21, 2001 now U.S. Pat. No. 6,662,802. These applications claim priorityof New Zealand Patent Nos. 505355, filed on Jun. 21, 2000 and 509040,flied on Dec. 20, 2000, all of which are hereby incorporated byreference in their entirety.

BACKGROUND TO THE INVENTION

1. Field of the Invention

The present invention relates to conduits and in particular to conduitsfor use in a breathing circuit.

2. Summary of the Prior Art

In assisted breathing, particularly in medical applications, gaseshaving high levels of relative humidity are supplied and returnedthrough conduits of a relatively restricted size. Build up ofcondensation-on the inside wall of the conduit is a frequent result ofthis high humidity. In the prior art, attempts have been made to reducethe adverse effect of this condensation by either reducing the level ofcondensation or providing collection points in the conduit for drainingcondensed liquid from the conduit. Reducing the condensation hasgenerally been by maintaining or elevating the temperature of the gasesflow and/or of the conduit wall to reduce the formation of condensation.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a conduit, whichwill at least go some way towards improving on the above or which willat least provide the public and the medical profession with a usefulchoice.

In a first aspect the invention consists in a method of conveying humidbreathing gases from a patient comprising:

providing a flexible breathing tube having a first end and a second endwherein said tube is connected to a patient interface at said first end;

conveying said breathing gases from said patient through said tube;

heating said gases in said tube;

transmitting at least some water vapour from said humid breathing gasesthrough the wall of said tube.

Preferably, said tube comprises an enclosing outer wall defining aflexible gases passageway between said first end and said second end,and

at least a region of said enclosing outer wall being of a material thatallows the transmission of water vapour without allowing thetransmission of liquid water or respiratory gases through said enclosingouter wall, and wherein said at least a region and said outlet areseparate from each other.

Preferably, said gases are heated by an elongate heater wire located insaid breathing tube.

Preferably, said heater wire lies freely within said passageway, suchthat heater wire settles over at least some of its length at low pointsin said passageway where condensed water vapour may collect.

Preferably, said breathing tube further including at least one helicallywound polymer tape or strip, part or all of said strip being of amaterial that allows the passage of water vapour without allowing thepassage of liquid water or respiratory gases, respective edges ofadjacent turns of said strip being adjoining or overlapping and bonded.

Preferably, said heater is covered with an inner hydrophobic insulatinglayer and at least partially covered with an outer hydrophilic layer,there being no direct supply of water to said hydrophilic layer fromoutside said tube.

Preferably, said heater wire lies freely within said passageway, suchthat heater wire settles over at least some of its length at low pointsin said passageway where condensed water vapour may collect.

In a further aspect said invention consists in a method of conveyinghumid breathing gases to and from a patient comprising:

providing a flexible coaxial breathing tube, having a patient end and adistal end, comprising:

-   -   an outer conduit having an enclosing outer wall,    -   an inner conduit having an enclosing wall, said inner conduit        located within said outer conduit,    -   a patient interface at said patient and,

supplying said breathing gases to said patient through a supplypassageway being one of said inner conduit or the space between saidinner conduit and said outer conduit,

returning gases from said patient through a return passageway being theother of said inner conduit or the space between said inner conduit andsaid outer conduit, heating said returning gases with a heater;

transmitting at least some water vapour from said returning gasesthrough the wall of said inner conduit.

Preferably, at least a region of said enclosing wall of said innerconduit being of a material that allows the transmission of water vapourwithout allowing the transmission of liquid water or respiratory gasesthrough said enclosing wall, and wherein said at least a region and theoutlet of said breathing tube are separate from each other.

Preferably, said returning gases are heated by a heater wire locatedwithin said return passageway.

Preferably, said heater wire lies freely within said return passageway,such that heater wire settles over at least some of its length at lowpoints in said return passageway where condensed water vapour maycollect.

Preferably, said inner conduit further including at least one helicallywound polymer tape or strip, part or all of said strip being of amaterial that allows the passage of water vapour without allowing thepassage of liquid water or respiratory gases, respective edges ofadjacent turns of said strip being adjoining or overlapping and bonded.

Preferably, said heater is covered with all inner hydrophobic insulatinglayer and at least partially covered with an outer hydrophilic layer,there being no direct supply of water to said hydrophilic layer fromoutside said breathing tube.

Preferably, said heater wire lies freely within said passageway, suchthat heater wire settles over at least some of its length at low pointsin said return passageway where condensed water vapour may collect.

Preferably, said breathing tube including said material is extruded.

Preferably, said inner conduit including said material is extruded.

To those skilled in the art to which the invention relates, many changesin construction and widely differing embodiments and applications of theinvention will suggest themselves without departing from the scope ofthe invention as defined in the appended claims. The disclosures and thedescriptions herein are purely illustrative and are not intended to bein any sense limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional elevation of a conduit for the expiratorylimb of a breathing circuit according to the present invention.

FIG. 2 is a cross sectional view of a section of conduit wall accordingto one possible construction.

FIG. 3 is a cross sectional view of a co extrusion die head forextruding a conduit including two longitudinal strips of permeablematerial, similar to the conduit of FIG. 1.

FIG. 4 is a cross sectional elevation of a coaxial breathing circuitaccording to a further embodiment of the present invention incorporatinga heated wick in the expiratory gases flow path.

FIG. 5 is a side elevation in partial cross section of a coaxialbreathing circuit including a heated wick in both the inspiratory andexpiratory gases flow paths.

FIG. 6 is a representation of a breathing circuit with an expiratorylimb fashioned according to the present invention and including a heatedwick according to a further aspect of the present invention.

FIG. 7 is a cut-away perspective view of a heated wick according to afurther aspect of the present invention

FIG. 8 is a side elevation partially in cross section of an expiratorylimb conduit according to a further embodiment of the present invention.

DETAILED DESCRIPTION

The present invention involves the provision of a heated wick within oneof the lengths of conduit making up a breathing circuit. By heated wickwe refer to a heater associated with a portion of hydrophilic material.The heated wick is disposed freely within the conduit so that at leastpart of it lays in low points of the conduit at which condensationaccumulates. Accumulated condensation is absorbed by the hydrophilicmaterial and re-evaporated by heat from the heater.

As seen in FIGS. 1A and 7 the heated wick 100 is comprised of an outerhydrophilic material 108 covering an inner insulating hydrophobic layer112 which in turn covers a heater element 110. Any water that collectsin the conduit 102 is attracted to and drawn into the hydrophilicmaterial 108, and is then re-vaporised as it is heated by the heaterelement 110. The intermediate hydrophobic insulating layer 112 isprovided to electrically insulate the inner heater element 110 from therest of the system.

Such a heated wick 100 as shown in FIG. 7 may be constructed byco-extruding the hydrophobic insulating layer 112 and hydrophilic layer108 onto the heater wire 110. Suitable materials for the hydrophiliclayer include polyester or polyurethane foam, or a braid of hydrophilicmaterial e.g cotton. Suitable materials for the hydrophobic layerinclude polypropylene or silicone coatings.

An alternate form for the heated wick is shown in each of FIGS. 1 b, 1 cand 1 d. In FIG. 1 b the heated wick includes a looped back heaterelement 110, coated in a hydrophobic insulating layer 112, and the wholeencased within a hydrophilic surrounding layer 108. In a furthervariation depicted in FIG. 1 c the heater element is an electricalresistance heater and includes a length 120 of higher resistance and alength 121 of lower resistance, insulated from one another and joined attheir remote ends. In a still further variation depicted in FIG. 1 d theheated wick 100 is disposed in the conduit as a simple loop. Each ofthese variations is provides both ends of the heated wick at the sameend of the conduit, allowing a single connection of the heater elementto an energising source. The embodiment of FIG. 1 c has the additionaladvantage that the heater element voltage at the remote end will belower than half the supply voltage, and with appropriate selection canbe very close to zero.

The heated wick may also be provided in both the inspiratory andexpiratory conduits. In this case a single length of heated wick may rundown the inspiratory conduit and back up the expiratory conduit, withthe ends of the conduits being insufficiently close proximity to enableeasy electrical connection to both ends.

The heated wick is provided with connections at its ends for connectingto an energising source. The ends of the wick may be directlyelectrically connected to electrical connectors in the connector of thetube or conduit. These connectors may for example be a socket forreceiving a plug from a voltage source. Alternatively the heated wickmay be a fixture of an assisted breathing device, such as a ventilatoror humidifier, and may extend from within the breathing conduitconnection port of the device, or be plugged into a socket within suchport. Many other configurations for supplying power to the heated wickwill also suggest themselves.

The heater element 110 is also effective to supply heat to the gasesstream to reduce the overall level of condensation occurring within theconduit. At the same time any condensation that does occur is sucked tipby the wick and re-evaporated by heat from the heater element 110.Accordingly where a heated wick is provided in the inspiratory arm ofthe breathing circuit humidity supplied to the gases stream prior toentry into the breathing circuit is not lost through condensation,instead being re-evaporated by the heated wick. This reduces the totalhumidification load of the breathing circuit as well as eliminating therequirement for conduit drainage ports.

Where the heated wick is provided in the expiratory conduit iteliminates the need for conduit drainage ports. Furthermore it providesadditional advantages when used in conjunction with an expiratoryconduit in which at least a part of the conduit wall is formed from abreathable material. Such an arrangement is shown in FIG. 6.

A breathable material, as used herein, is a material that allows thepassage of water vapour without allowing the passage of liquid water orrespiratory gases. Materials may be breathable due to their composition,physical structure a combination thereof.

One such breathable material is an activated perfluorinated polymermaterial having extreme hydrophilic properties. An example of thispolymer material is marketed under the trade mark NAFION by DuPontFluoro products of Fayetteville USA. This material is useful due to itsextreme hydrophilic properties and due to its ability to be extruded,particularly to be co-extruded in combination with other plasticmaterials.

Alternative materials are also envisaged including:

(a) Hydrophilic thermoplastics,

(b) woven treated fabric products exhibiting breathable characteristics

The preferred material is a hydrophilic polyester block copolymer formedinto a homogeneous flat film. An example of such a film is sold underthe brand SYMPATEX. This material is particularly suited to thin filmproductions.

An example of application of the conduit with heated wick is shown inFIG. 6. A heater element 110 coated with a hydrophilic material, runsthe length of the semi-permeable conduit 102 and the inspiratory conduit101. During operation humidified gases are drawn through inspiratoryconduit 101, then flow through the I′ connector 103, and are thendelivered to the patient (not shown). When the patient expires the gasesflow through the T connector 103, and then flow through the breathableexpiratory conduit 102. The expiratory gases will be almost saturatedwith humidity and as the wall of the breathable expiratory conduit 102will be relatively cool, some portion of the vapour in the gases willcondense and therefore water will collect in the conduit and run towardsthe lowest point 106. As already mentioned such collection of water isundesirable and therefore the heated wick 100 is provided to revaporisethe water that collects. This is particularly important where thebreathable material is one, such as SYMPATEX, which transmits watervapour but does not transmit liquid water. While such materials areadvantageous for their ability to stop harmful bacteria and viruses thisadvantage is offset by their inability to transmit liquid water. Byre-evaporation of any collected water by the heated wick it can betransmitted through the breathable membrane in its vapour state.

Referring to FIG. 1, in one embodiment, the conduit 4 of the expiratorylimb of a breathing circuit is formed having one or more longitudinalstrips 2, 3 of semi permeable membrane as part of the wall 1 thereof.

Referring to FIG. 8 an alternative embodiment of the expiratory limbconduit is shown in which the entire flexible wall membrane of theconduit is formed from a breathable plastic membrane, extruded and woundhelically with edges of adjacent turns sealed to one another.

Referring to FIGS. 4 and 5, further aspects is shown in which anexpiratory limb conduit according to the present invention is providedas a gases flow path of a coaxial conduit configuration, such thatexpiratory gases and inspiratory gases each flow in one of the innerconduit or the space between the inner conduit and the outer conduit andin use water vapour but not liquid water is transmitted from theexpiratory gases passageway to the inspiratory gases passageway.

Referring to FIGS. 2 & 8, spiral or helical internal (or external)reinforcing members 30, or a series of annular hoop reinforcing members,may be provided outside (or inside) the tubular membrane 6 to providesupport to it. The helical, spiral or hoop supporting members may forexample be formed from polymer plastic materials, such as the materialused in the wall of the conduit (not being the semi permeable regions),or alternatively may for example be a metal wire support, such as drawnsteel wire.

The conduit shown in FIG. 2 may be formed in any one of a number ofmethods. For example the tubular membrane 6 may be supplied in acontinuous tube. Alternatively it might be supplied in tape form whichmay result in the conduit of FIG. 8. Supplied as extruded tape 81, themembrane may be wound helically onto a former. The helical supportingrib 30, provided in a semi molten state is then laid on the overlapbetween adjacent turns. The heat from the helical supporting rib 30bonds the two adjacent strips with itself forming a flexible resilientconduit once cooled.

Referring to FIG. 8 an additional longitudinal reinforcement may beprovided to alleviate the shortcomings of some of the breathablematerials. This reinforcement may be in the form of a plurality ofreinforcing threads 83. The threads 83 run parallel to the length of theconduit and are supported on the helical reinforcing ribs, spanningbetween them. As many threads may be provided. For example eight threadsmay be spaced around the circumference of the tube. The reinforcingthreads 83 stop accidental stretching of the conduit, and providing theyhave some stiffness and the rib spacing is not to large, also reduce anylongitudinal compression of the conduit under negative relative internalpressures.

Referring to FIG. 3 the conduit, such as that shown in FIG. 1, mayalternatively be formed by co extrusion of the semi permeable material(where the material is a suitable extrudable material) with a plasticmaterial forming the remainder of the conduit wall. A suitable coextrusion die 9 is depicted in FIG. 3 in which a pair of circumferentialsections 7 of the die opening have the semi permeable plastic materialextruded therethrough, and the remainder sections 8 of the annularextrusion opening have the non permeable plastic wall material extrudedtherethrough.

The purpose of the breathable region or regions of the conduit wall isto allow diffusion of water vapour (and for some materials liquid water)from the expiratory limb of the breathing circuit along the path thereofindependent of specific drain locations. This eliminates the build up ofcondensation within the expiratory limb by drying the humidified gasesduring their flow through the expiratory limb. This furthermore reducesthe humidity of the gases arriving at ancillary equipment, such asfilters, ventilators and the like reducing the risk of condensationaccumulation, thereby improving their operation.

In accordance with a further aspect of the invention, and as exemplifiedin FIGS. 4 and 5 the conduit incorporating one or more longitudinalstrips of semi permeable membrane may further be incorporated in acoaxial breathing circuit as a passive humidification device. Inparticular referring to the cross section in FIG. 4 the coaxialbreathing circuit may include an outer conduit 11 and an inner conduit10. Preferably, for heat transfer reasons, the inner conduit 10 carriesthe inspiratory flow in the space 12 there within. The expiratory flowis carried in the space 13 between the inner conduit 10 and the outerconduit 11, and a doubled back heated wick 100 is provided in theexpiratory flow space. The airflow configuration is indicated by arrows20, 19 respectively in FIG. 5.

The inner conduit 10 is formed having one or more longitudinal strips 2,3 of semi permeable membrane in the wall 1 thereof, as has previouslybeen described with reference to FIGS. 1, 2 and 3. Thus humidity in theexpiratory flow space 13 may pass through the sections 2, 3 of semipermeable membrane to humidify the inspiratory flow in inspiratory flowspace 12.

The semi permeable membrane works on relative partial pressures of watervapour so, with the flows in a counter flow arrangement substantialpassive humidification of the inspiratory flow can be achieved.

Referring to FIG. 5 a circuit configuration including the coaxialconduit depicted in FIG. 4 is represented, but with a heated wick 100disposed in both of the inspiratory and expiratory flow paths (forexample doubling back at the patient end connector 15. In this circuitthe conduit has a patient end connector 15 and a ventilator endconnector 16 having inspiratory port 17 and an expiratory port 18. Theinspiratory 20 and expiratory 19 counter flows are indicated.

So in its broadest form the invention is a conduit for a breathingcircuit which includes a heater associated, at least in part with aportion of hydrophilic material. The purpose of the heater is toevaporate any condensed liquid collecting in the conduit. The heatedwick is not a humidifier and so no liquid is supplied directly to thehydrophilic material from outside said conduit. The heated wick reducesthe risk of collected water being passed to the patient and causingchoking fits or discomfit. It also improves the predictability of thehumidity levels in the gases passed to the patient. It is preferred thatthe heated wick lies freely in the conduit to settle at low points inthe conduit where condensation may collect.

Where the conduit in question is an expiratory conduit, or at leastwhere the heated wick is located in an expiratory flow path of abreathing circuit, then the heated wick will have additional benefitswhere the conduit has at least of potion of its wall formed frombreathable material for passive dehumidification of the expired gases.Because the breathable material will pass only vapour, evaporation ofany condensed liquid within the conduit will allow that liquid tosubsequently be passed.

Another aspect to the invention is the construction of the heated wick,which is preferably an elongate heating element covered with an innerhydrophobic insulating layer co-extruded with an outer hydrophiliclayer.

It will be appreciated that the concepts encapsulated by the describedand illustrated embodiments are not restricted to being combined only asdescribed. For example the heated wick described with reference to FIGS.6 and 7 may be used in the coaxial conduit of FIGS. 4 and 5 or theseparate limbed conduit as in FIG. 6. Similarly the conduitincorporating the breathable membrane, whether it be the inner conduitof the coaxial configuration shown in FIGS. 4 and 5 or the stand aloneexpiratory limb of FIG. 6, may be formed as a co-extrusion as in FIGS. 1and 3 or as an extruded tape as in FIG. 8 and with the breathablemembrane being of a number of alternate materials. While someembodiments have been described as preferred and convey particularadvantages over other embodiments many other combinations may provecommercially useful.

1. A method of conveying humid breathing gases from a patientcomprising: providing a flexible breathing tube having a first end and asecond end wherein said tube is connected to a patient interface at saidfirst end; conveying said breathing gases from said patient through saidtube; heating said gases in said tube; transmitting at least some watervapour from said humid breathing gases through the wall of said tube. 2.A method of conveying humid breathing gases as claimed in claim 1,wherein said tube comprises an enclosing outer wall defining a flexiblegases passageway between said first end and said second end, and atleast a region of said enclosing outer wall being of a material thatallows the transmission of water vapour without allowing thetransmission of liquid water or respiratory gases through said enclosingouter wall, and wherein said at least a region and said outlet areseparate from each other.
 3. A method of conveying humid breathing gasesas claimed in claim 2, wherein said gases are heated by an elongateheater wire located in said breathing tube.
 4. A method of conveyinghumid breathing gases as claimed in claim 3, wherein said heater wirelies freely within said passageway, such that heater wire settles overat least some of its length at low points in said passageway wherecondensed water vapour may collect.
 5. A method of conveying humidbreathing gases as claimed in claim 2, wherein said breathing tubefurther including at least one helically wound polymer tape or strip,part or all of said strip being of a material that allows the passage ofwater vapour without allowing the passage of liquid water or respiratorygases, respective edges of adjacent turns of said strip being adjoiningor overlapping and bonded.
 6. A method of conveying humid breathinggases as claimed in claim 3, wherein said heater is covered with aninner hydrophobic insulating layer and at least partially covered withan outer hydrophilic layer, there being no direct supply of water tosaid hydrophilic layer from outside said tube.
 7. A method of conveyinghumid breathing gases as claimed in claim 6, wherein said heater wirelies freely within said passageway, such that heater wire settles overat least some of its length at low points in said passageway wherecondensed water vapour may collect.
 8. A method of conveying humidbreathing gases to and from a patient comprising: providing a flexiblecoaxial breathing tube, having a patient end and a distal end,comprising: an outer conduit having an enclosing outer wall, an innerconduit having an enclosing wall, said inner conduit located within saidouter conduit, a patient interface at said patient and, supplying saidbreathing gases to said patient through a supply passageway being one ofsaid inner conduit or the space between said inner conduit and saidouter conduit, returning gases from said patient through a returnpassageway being the other of said inner conduit or the space betweensaid inner conduit and said outer conduit, heating said returning gaseswith a heater; transmitting at least some water vapour from saidreturning gases through the wall of said inner conduit.
 9. A method ofconveying humid breathing gases as claimed in claim 8, wherein at leasta region of said enclosing wall of said inner conduit being of amaterial that allows the transmission of water vapour without allowingthe transmission of liquid water or respiratory gases through saidenclosing wall, and wherein said at least a region and the outlet ofsaid breathing tube are separate from each other.
 10. A method ofconveying humid breathing gases as claimed in claim 9, wherein saidreturning gases are heated by a heater wire located within said returnpassageway.
 11. A method of conveying humid breathing gases as claimedin claim 10 wherein said heater wire lies freely within said returnpassageway, such that heater wire settles over at least some of itslength at low points in said return passageway where condensed watervapour may collect.
 12. A method of conveying humid breathing gases asclaimed in claim 8, wherein said inner conduit further including atleast one helically wound polymer tape or strip, part or all of saidstrip being of a material that allows the passage of water vapourwithout allowing the passage of liquid water or respiratory gases,respective edges of adjacent turns of said strip being adjoining oroverlapping and bonded.
 13. A method of conveying humid breathing gasesas claimed in claim 10, wherein said heater is covered with an innerhydrophobic insulating layer and at least partially covered with anouter hydrophilic layer, there being no direct supply of water to saidhydrophilic layer from outside said breathing tube.
 14. A method ofconveying humid breathing gases as claimed in claim 13, wherein saidheater wire lies freely within said passageway, such that heater wiresettles over at least some of its length at low points in said returnpassageway where condensed water vapour may collect.
 15. A method ofconveying humid breathing gases as claimed in claim 2, wherein saidbreathing tube including said material is extruded.
 16. A method ofconveying humid breathing gases as claimed in claim 8, wherein saidinner conduit including said material is extruded.